Cochrane Gambit

The Cochrane Gambit is a speculative knight sacrifice that arises in the Petroff Defence: 1.e4 e5 2.Nf3 Nf6 3.Nxe5 d6 and now 4.Nxf7!?

Black has no good alternative to taking the knight, and White is left with two pawns and an exposed black king as compensation for the sacrificed knight. Rather than striving for a quick attack on the black king, White will typically aim to build up a strong centre, while Black's natural development plans are disrupted by the misplaced black king, and Black will often spend tempi moving the king to a relatively safe position, allowing White to accumulate a space advantage and initiative in the meantime. In some games White completely crushes Black by pushing the central pawns forward, forcing Black to make heavy concessions.

The above position is a good illustration of the sort of trouble that Black can get into. Even though Black has succeeded in exchanging queens and remains a piece ahead for just two pawns, White is close to winning due to the powerful central pawns and kingside pressure.

The Cochrane Gambit is probably not completely sound, so players after a completely sound antidote to the Petroff may be advised to look at, for instance, Michael Goeller's 3.d4 repertoire or the line 4.Nf3 Nxe4 5.Nc3 Nxc3 6.dxc3, which gives White the opportunity to castle queenside and, if Black castles short, roll the kingside pawns forward. However, I think the Cochrane is close enough to being fully sound to be a perfectly viable weapon at club level (and maybe a fair way beyond that).

Important lines and ideas

After the obligatory 4...Kxf7, White should avoid 5.Bc4+ as it is met by the strong 5...d5, attacking the white bishop and striking out in the centre, giving Black easy play. The usual move for White is instead 5.d4, with the idea that 5...Nxe4?! doesn't work because of 6.Qh5+ which results in White picking up the knight on e4 after 6...g6 7.Qd5+ or 6...Ke7 7.Qe2.

Most of Black's responses to 5.d4 allow White to get sufficient compensation for the sacrificed knight. 5...d5 6.e5 Ne4 leaves Black's knight in an unstable position after 7.Bd3. 5...Be7 can be followed up with the idea of "castling by hand" with ...Re8 and ...Kg8, but in the meantime White can build up a strong centre. 6.Nc3 c6 (or 6...Re8 7.Bc4+ Kf8 8.0-0) 7.Bd3 Re8 8.0-0 Kg8 9.h3 are typical sample lines, with White enjoying considerable compensation for the piece.5...Qe8 has been given as better for Black in some sources, but I am not convinced. Black increases the pressure against e4, but 6.Nc3 d5 (6...c5 is suggested by Watson but then both 7.Be3!? and 7.Bc4+ Be6 8.d5 are quite good.) 7.e5 gives White good play.

The main theoretical problem, as far as I can see, is 5...g6 6.Nc3 (6.Bc4+ Kg7 7.Nc3 Be7 is also unconvincing) 6...c5 which intends to tuck the black king away on g7, while undermining White's d4-pawn. White retains practical chances due to Black's exposed king but theoretically the resulting positions appear to slightly favour Black. Black can also play 5...c5 but this gives White the additional possibility 6.dxc5 (6.Bc4+ is met by 6...d5 7.exd5 b5) 6...Nc6 7.Bc4+ Be6 8.Bxe6+ Kxe6, where White has more in the way of chances due to Black's exposed king. In that line, however, Black also has 6...d5!? which may suffice for a theoretical edge.

White's main alternative is 5.Nc3, which usually transposes to 5.d4 lines with Nb1-c3, following a subsequent d2-d4, since if White holds back with the d-pawn then this hinders White's ability to crush Black using the central pawns. I haven't been able to find a convincing way for White to avoid transposing into the problematic 5.d4 g6 6.Nc3 c5 line, but it appears that White can get good compensation for the sacrificed knight against other responses by Black.